# Does the angles of incidence affect speed in glass

1. Jan 10, 2016

### bmcd

I understand that the refractive index of different materials affects the speed of light but does light change speed in glass when entering from air at different angles of incidence?? if not what causes the variation in lateral displacement?

2. Jan 10, 2016

### blue_leaf77

Do you mean, whether the light speed in the glass is dependent on the angle at which it impinges on the glass interface? If yes, it is not. The velocity in a medium other than air is given by $v=c/n$, no angle dependence.
Which particular arrangement are you talking about?

3. Jan 11, 2016

### bmcd

Ok, thanks but why the variation in lateral displacement

4. Jan 11, 2016

### blue_leaf77

Can you give a physical example pertaining the lateral displacement you are talking about?

5. Jan 11, 2016

### bmcd

light passes into a glass block at 50 degrees will have a larger lateral displacement than light passing through the same glass block at a lesser angle of incidence. Why is this?

6. Jan 11, 2016

### jbriggs444

Are you, for instance, talking about viewing a page of text through a fish tank or a thick pane of glass and noticing that the position of the [image of the] text seems displaced to the right when viewing through a tank slanted away to the right and is displaced to the left when viewing through a tank that is slanted away to the left?

It seems that you are. No, the speed of light in a particular type of glass is what it is, independent of the angle of incidence.

Read up on Snell's law. Do the trigonometry. Draw some lines and see what happens. One intuitive approach is to note that when the light impacts perpendicular to the surface there is no displacement and that when it impacts at any other angle there is. Obviously there will be a smooth curve that describes the offset as a function of refractive index, angle of incidence and block thickness that matches these simple observations. None of this requires a variation in speed of light according to angle of incidence.

7. Jan 11, 2016

### bmcd

Thanks for your help, I'm referring to a simple Ray box and changing the angle of incidence. With a greater AOI the distance between the emergent Ray and the original path of light increases as you increase the AOI.

8. Jan 11, 2016

### bmcd

What is the science behind the difference in distance between the emergent Ray and the original path of light before refraction at different angles of incidence using a Ray box and a glass block? i.e bigger angle of incidence equals a bigger distance between those two points than a smaller angle of incidence!

Sorry not a physics specialist!

9. Jan 11, 2016

### blue_leaf77

Are you familiar with geometry? What do you think when you see this image
?
How will you express $d$ in terms of the other given parameters in that picture?

10. Jan 11, 2016

### bmcd

Yes this is what I'm talking about so in layman terms why is d different at different angles of incidence

11. Jan 11, 2016

### jbriggs444

What is d when the angle of incidence is 90 degrees?
Is d non-zero at other angles of incidence?
Do you expect d to vary continuously with the angle of incidence?

12. Jan 12, 2016

### bmcd

Yes it is zero perpendicular to the glass block but it changes at different angles below 90. I suppose what I'm asking is there a relationship between the angle of incidence and refraction from air to glass (in basic GCSE) terminology?

13. Jan 12, 2016

### ehild

Do you know Snell's Law? (The relation between angle of incidence and angle of refraction?)
When the angle of incidence changes, so does the angle of refraction. The length of path inside the gas plate also changes. Why do you think d must be constant? It is an easy geometric derivation to get the distance d in terms of angle of incidence.

14. Jan 12, 2016

### blue_leaf77

@bmcd , I guess your first keyword for now is the "Snell's law".